In recent years, in high speed & high density signal transmission between electronic devices and between wiring boards, transmission through conventional electric wirings is restricted in a rise in a speed and a density due to barriers brought about by mutual interference and attenuation of signals. In order to break through the above barriers, a technique for connecting electronic devices and printed wiring boards with each other by means of light, so-called optical interconnection is investigated. A polymer optical waveguide attracts attentions as an optical transmission line in terms of easier processing, a lower cost, a higher freedom of wirings and a possible rise in a density. A type in which a polymer optical waveguide is prepared on a glass epoxy resin substrate assuming that it is applied to a photoelectric composite board and a flexible type having no rigid support base assuming that boards are connected with each other are worked out as the form of the polymer optical waveguide.
A high heat resistance in addition to a high transparency (low optical transmission loss) is required to a polymer optical waveguide from the viewpoints of use environment of appliances to which it is applied and mounting of parts, and (meth)acrylic polymers are known as a material for the above optical waveguide (refer to, for example, patent documents 1 and 2). The (meth) acrylic polymers have a high transparency of 0.3 dB/cm in a wavelength of 850 nm, but the evaluations of the heat resistance, for example, the specific test results of an optical transmission loss after a solder reflow test and the like are not specifically described therein and are not clear.
Resin compositions containing a carboxylic acid-modified phenoxy resin are known as a light-sensitive resin composition which is excellent in a heat resistance and which can be developed by an alkaline aqueous solution (refer to, for example, patent documents 3 and 4). However, the above resin compositions have been invented for plating resists in a production process for printed wiring boards, and they are excellent in a heat resistance but low in a transparency and are not suitable as a resin composition for an optical material.    Patent document 1: Japanese Patent Application Laid-Open No. 258537/1994    Patent document 2: Japanese Patent Application Laid-Open No. 195079/2003    Patent document 3: Japanese Patent Application Laid-Open No. 47383/2000    Patent document 4: Japanese Patent Application Laid-Open No. 147765/2000